1. Field of the Invention
This invention relates to an improved particulate handling apparatus and a method of using that apparatus. The invention relates especially but not exclusively to apparatus suitable for handling particulates, which have been imparted with a high kinetic energy due handling procedures.
2. State of the Art
Particulates, which from hereon are referred to a “pellets”, (which is a term used to describe particulates in general) are often conveyed pneumatically using a gas to entrain the solids. Such pneumatic conveyance systems are used to transfer pellets between containers, for example from chemical reactors to drums or vice versa. When the pellets are a catalyst the transfer of pellets may be in order to load a reactor vessel, or unload a reactor vessel to allow treatment of the catalyst or re-bedding of the catalyst.
Known methods of for example loading catalyst beds involve lifting bulk containers containing pellets and loading a catalyst bed by allowing the pellets to flow into the catalyst bed by means of a flexible sock. Such systems have the disadvantage of having to use a crane to lift material before it can be transferred. Consequently, pneumatic systems for transfer of material have been developed, which avoid the need for craning.
Pneumatic systems involve vacuuming catalyst pellets from ground level to an interceptor or separator above the catalyst bed but again such systems use the free fall of the catalyst pellets through a flexible sock to load the catalyst bed. Further, a primary objective for a pneumatic conveying system is to convey the pellets at the highest possible rate to maximize transfer, which saves time and therefore reduces the cost of handling material. To do this, the entrained pellet gas mixture is forced through piping, conduits or ducting at the highest possible velocity. A problem, however, with such an approach is that the higher the velocity of transportation of the pellets, the greater the kinetic energy each pellet acquires. When the pellet and entrainment gas mixture reaches the location where the pellets are to be discharged, for instance into a drum or a reactor, the entrainment gas is separated from the pellets and the pellets moved to their desired position.
Once the entrainment gas has been separated from the pellets, the kinetic energy possessed by the pellets needs to be reduced and transferred from the pellets. In previously known particulate handling apparatus, and in particular, catalyst pellet handling apparatus, this transfer has been via friction with a gas whilst the pellet is in motion through said gas within a loading hopper and/or by impacting a surface of the loading hopper. This method of transfer of kinetic energy from the pellets is only suitable for pellets where the impact force experienced by the pellets is not sufficiently great to physically damage the pellets. It has been found that large pellets, for example 3-16 mm in their greatest dimension, or particularly dense pellets gain sufficient kinetic energy during transportation that the current methods of reducing the kinetic energy in the pellets is insufficient. This has the result that when the pellets impact a surface of the loading hopper, cracking or fragmentation of the pellets occurs. This is clearly undesirable as it greatly shortens the life of the pellets and where the pellets are catalysts, lessens the efficiency of the catalyst when it is working.
Another known method of reducing the kinetic energy associated with pellets is to use a baffle in a piping that is used to separate the pellets prior to the pellets being transferred to a hopper to feed a catalyst reactor vessel. However, this has the disadvantage that because the separator is upstream of the hopper, there may be loss of some of the lighter particulate material before it reaches the hopper. This has the disadvantage that as a result of loss of material the processing of the material is less cost effective. Also, having a separation means and baffles, which are separate from the hopper means that the whole system is more cumbersome and less portable. Further, when baffling of the material occurs before the material enters a hopper, there is a need to ensure that any particulate material that is lost is captured or vented from the operation site to avoid environmental contamination.